http2/hpack: build static table with go generate

As the static version of headerFieldTable in hpack is generated in runtime,
we may use the go:generate to prepare the struct before the initialization phase.
This is supposed to save init time and allocations for many binaries,
as net/http imports hpack.

Before:
init golang.org/x/net/http2/hpack @1.1 ms, 0.097 ms clock, 21240 bytes, 29 allocs
After:
init golang.org/x/net/http2/hpack @0.67 ms, 0.015 ms clock, 8120 bytes, 9 allocs

Fixes golang/go#55881

Change-Id: Ia6575f67ffcba7cc4d75899b24a9c56deb58ccac
Reviewed-on: https://go-review.googlesource.com/c/net/+/434875
Run-TryBot: Damien Neil <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: Thorleon

http2/hpack/gen.go

@@ -0,0 +1,184 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"io/ioutil"
+	"os"
+	"sort"
+
+	"golang.org/x/net/http2/hpack"
+)
+
+// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-07#appendix-B
+var staticTableEntries = [...]hpack.HeaderField{
+	{Name: ":authority"},
+	{Name: ":method", Value: "GET"},
+	{Name: ":method", Value: "POST"},
+	{Name: ":path", Value: "/"},
+	{Name: ":path", Value: "/index.html"},
+	{Name: ":scheme", Value: "http"},
+	{Name: ":scheme", Value: "https"},
+	{Name: ":status", Value: "200"},
+	{Name: ":status", Value: "204"},
+	{Name: ":status", Value: "206"},
+	{Name: ":status", Value: "304"},
+	{Name: ":status", Value: "400"},
+	{Name: ":status", Value: "404"},
+	{Name: ":status", Value: "500"},
+	{Name: "accept-charset"},
+	{Name: "accept-encoding", Value: "gzip, deflate"},
+	{Name: "accept-language"},
+	{Name: "accept-ranges"},
+	{Name: "accept"},
+	{Name: "access-control-allow-origin"},
+	{Name: "age"},
+	{Name: "allow"},
+	{Name: "authorization"},
+	{Name: "cache-control"},
+	{Name: "content-disposition"},
+	{Name: "content-encoding"},
+	{Name: "content-language"},
+	{Name: "content-length"},
+	{Name: "content-location"},
+	{Name: "content-range"},
+	{Name: "content-type"},
+	{Name: "cookie"},
+	{Name: "date"},
+	{Name: "etag"},
+	{Name: "expect"},
+	{Name: "expires"},
+	{Name: "from"},
+	{Name: "host"},
+	{Name: "if-match"},
+	{Name: "if-modified-since"},
+	{Name: "if-none-match"},
+	{Name: "if-range"},
+	{Name: "if-unmodified-since"},
+	{Name: "last-modified"},
+	{Name: "link"},
+	{Name: "location"},
+	{Name: "max-forwards"},
+	{Name: "proxy-authenticate"},
+	{Name: "proxy-authorization"},
+	{Name: "range"},
+	{Name: "referer"},
+	{Name: "refresh"},
+	{Name: "retry-after"},
+	{Name: "server"},
+	{Name: "set-cookie"},
+	{Name: "strict-transport-security"},
+	{Name: "transfer-encoding"},
+	{Name: "user-agent"},
+	{Name: "vary"},
+	{Name: "via"},
+	{Name: "www-authenticate"},
+}
+
+type pairNameValue struct {
+	name, value string
+}
+
+type byNameItem struct {
+	name string
+	id   uint64
+}
+
+type byNameValueItem struct {
+	pairNameValue
+	id uint64
+}
+
+func headerFieldToString(f hpack.HeaderField) string {
+	return fmt.Sprintf("{Name: \"%s\", Value:\"%s\", Sensitive: %t}", f.Name, f.Value, f.Sensitive)
+}
+
+func pairNameValueToString(v pairNameValue) string {
+	return fmt.Sprintf("{name: \"%s\", value:\"%s\"}", v.name, v.value)
+}
+
+const header = `
+// go generate gen.go
+// Code generated by the command above; DO NOT EDIT.
+
+package hpack
+
+var staticTable = &headerFieldTable{
+	evictCount: 0,
+	byName: map[string]uint64{
+`
+
+//go:generate go run gen.go
+func main() {
+	var bb bytes.Buffer
+	fmt.Fprintf(&bb, header)
+	byName := make(map[string]uint64)
+	byNameValue := make(map[pairNameValue]uint64)
+	for index, entry := range staticTableEntries {
+		id := uint64(index) + 1
+		byName[entry.Name] = id
+		byNameValue[pairNameValue{entry.Name, entry.Value}] = id
+	}
+	// Sort maps for deterministic generation.
+	byNameItems := sortByName(byName)
+	byNameValueItems := sortByNameValue(byNameValue)
+
+	for _, item := range byNameItems {
+		fmt.Fprintf(&bb, "\"%s\":%d,\n", item.name, item.id)
+	}
+	fmt.Fprintf(&bb, "},\n")
+	fmt.Fprintf(&bb, "byNameValue: map[pairNameValue]uint64{\n")
+	for _, item := range byNameValueItems {
+		fmt.Fprintf(&bb, "%s:%d,\n", pairNameValueToString(item.pairNameValue), item.id)
+	}
+	fmt.Fprintf(&bb, "},\n")
+	fmt.Fprintf(&bb, "ents: []HeaderField{\n")
+	for _, value := range staticTableEntries {
+		fmt.Fprintf(&bb, "%s,\n", headerFieldToString(value))
+	}
+	fmt.Fprintf(&bb, "},\n")
+	fmt.Fprintf(&bb, "}\n")
+	genFile("static_table.go", &bb)
+}
+
+func sortByNameValue(byNameValue map[pairNameValue]uint64) []byNameValueItem {
+	var byNameValueItems []byNameValueItem
+	for k, v := range byNameValue {
+		byNameValueItems = append(byNameValueItems, byNameValueItem{k, v})
+	}
+	sort.Slice(byNameValueItems, func(i, j int) bool {
+		return byNameValueItems[i].id < byNameValueItems[j].id
+	})
+	return byNameValueItems
+}
+
+func sortByName(byName map[string]uint64) []byNameItem {
+	var byNameItems []byNameItem
+	for k, v := range byName {
+		byNameItems = append(byNameItems, byNameItem{k, v})
+	}
+	sort.Slice(byNameItems, func(i, j int) bool {
+		return byNameItems[i].id < byNameItems[j].id
+	})
+	return byNameItems
+}
+
+func genFile(name string, buf *bytes.Buffer) {
+	b, err := format.Source(buf.Bytes())
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if err := ioutil.WriteFile(name, b, 0644); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}